Sand lock valve

ABSTRACT

A singular piston included behind a valve seat within a gate valve assembly can be energized by external pressure through a hydraulic port within the valve body. When the back side of the singular piston is energized, the singular piston applies force in one direction against the adjacent valve seat, valve gate, opposing valve seat and valve seat pocket in both the valve open position and the valve closed position to block any unwanted matter from moving into the valve backside cavity. A singular piston has a pressure sealing surface and a piston pocket with an adjacent pressure sealing surface that allows the valve to seal in the closed position with the contained fluid bore pressure against the opposing valve body flow path side to the piston without the piston being energized.

CROSS-REFERENCE

This application is a continuation of U.S. application Ser. No.17/807,381, filed Jun. 17, 2022, which claims priority to U.S.Provisional Application Ser. No. 63/214,674, filed Jun. 24, 2021, thecontents of which are incorporated herein in their entirety byreference.

FIELD OF THE INVENTION

This disclosure relates generally to oil and gas equipment, and moreparticularly to an apparatus and method to prevent unwanted matter fromentering the valve backside cavity of a gate valve typically used forfracking a wellbore using a pressure actuated sealing mechanismincorporated within a gate valve. The described disclosure can be usedfor all gate valves that are rigged up on surface of the frack locationso as to deliver the medium into the wellbore so as to frack theformation in a safer and more efficient manner.

BACKGROUND OF THE INVENTION

Conventional gate valves that are rigged up on surface to deliver themedium and pressure required to frack the wellbore. When pumping themedium under pressure through the conventional gate valves, the mediumwhich is typically a fine mesh sand, builds up on the back side cavityof the gate valve. This causes the gate valve to be packed off with sandand can cause the valve to become stuck in the open or closed position.The fine mesh sand can also cause abrasive damage to the internalcomponents of the valve which leads to the valve to leak under pressurein the closed and open position. Another issue that can occur, thepacking that seals the internal pressure of the valve can fail whichcauses the valve to leak out to the location. These situations areextremely dangerous to the workers, will pollute the environment andcost the operator a lot of downtime and added expense.

For example, FIG. 6 shows a conventional gate valve assembly in an openposition. The conventional gate valve assembly is formed from a valvebody 31, which has an upstream passage 30 and a downstream passage 29.Both the upstream passage 30 and the downstream passage 29 areconcentrically located to each other and allow the medium (i.e., fluidsand mix) to pass through the valve body 31 in the open position. Fluidsand mix can enter from the upstream passage 30 and exit the downstreampassage 29. Alternatively, the fluid sand mix can enter from thedownstream passage 29 and exit the upstream passage 30 in the openposition.

Upstream seat pocket 37 is formed into the valve body 31 and locatedconcentrically to the upstream passage 30 at the upstream passage 30side of the valve body 31. Upstream seat 27 is located concentrically tothe upstream seat pocket 37 and is disposed partially within theupstream seat pocket 37. Downstream seat pocket 38 is formed into thevalve body 31 and located concentrically to the downstream passage 29 atthe downstream passage 29 side of the valve body 31. Downstream seat 33is located concentrically to the downstream seat pocket 38 and isdisposed partially within the downstream seat pocket 38. The gate 25 isin the open position and is located between upstream seat 27 anddownstream seat 33.

The fluid sand mix in the conventional valve assembly of FIG. 6 canenter the upper backside void 26 and the lower backside void 32 and candamage the upper valve stem packing 24 and lower valve stem packing 34.Once both upper valve stem packing 24 and lower valve stem packing 34are damaged, the conventional gate valve will leak to the outside ofvalve body 31.

Moreover, the fluid sand mix enters the upper backside void 26 and thelower backside void 32 under very high pressure and velocity, which inturn causes the sealing faces and components to erode due to a“sandblasting” effect.

Another common failure of a conventional gate valve is when the fluidsand mix enters the upper backside void 26 and the lower backside void32 under very high pressure and velocity and “packs off” within theupper backside void 26 and the lower backside void 32, which stops thegate 25 from moving between the open position as shown in FIG. 6 and theclosed position and FIG. 7 .

FIG. 7 shows the conventional gate valve in the closed position. Whenthe fluid sand mix enters the valve body 31 through the upstream passage30, the gate 25 is pushed up against the downstream seat 33 anddownstream seat pocket 38. A seal is formed between gate 25, downstreamseat 33, and downstream seat pocket 38. The fluid sand mix now cannotcommunicate with the downstream passage 29. However, a gap is createdbetween upstream seat pocket 37, upstream seat 27, and upstream passageside of gate 25. The fluid sand mix can now enter the upper backsidevoid 26 and the lower backside void 32, which will cause theconventional gate valve to fail as it would in the open position.

When the fluid sand mix enters the valve body 31 through the downstreampassage 29, the gate 25 is pushed up against the upstream seat 27 andupstream seat pocket 37. A seal is formed between gate 25, upstream seat27 and upstream seat pocket 37. The fluid sand mix now cannotcommunicate with the upstream passage 30. However, a gap is createdbetween downstream seat pocket 38, downstream seat 33, and downstreampassage 29 side of gate 25. The fluid sand mix can now enter the upperbackside void 26 and the lower backside void 32, which will cause theconventional gate valve to fail as it would in the open position.

The conventional valve now cannot seal in the closed position shown inFIG. 7 , and the fracking operation is halted. The conventional valvenow has to be replaced on the fracking location, which is extremelydangerous to personal life and the environment and is extremely costly.

One method currently used to mitigate the fine mesh sand from gettinginto the back side cavity of the gate valve is to pump grease into theback side cavity under pressure. Unfortunately, this method does notmitigate the problem completely and the medium still finds its way intothe back side cavity of the gate valve and causes the valve to fail.Also pumping the specialized grease into the back side of the valve iscostly due to the continuous pumping of grease and amount of greaserequired to fill the back side cavity.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more detailed description of the embodiments of the presentdisclosure, reference will now be made to the accompanying drawings,wherein:

FIG. 1 is a cross-sectional view of a gate valve assembly in the openposition according to the present disclosure.

FIG. 2 is a partial view of the inner assembly of FIG. 1 .

FIG. 3 is a cross-sectional view of a gate valve assembly in the openposition according to the present disclosure including a hydraulicassembly and upper and lower bonnets.

FIG. 4 is a cross-sectional view of a gate valve assembly in the closedposition according to the present disclosure including the hydraulicassembly and upper and lower bonnets.

FIG. 5 is a partial view of the inner assembly of FIG. 4 .

FIG. 6 is a cross-sectional view of a conventional gate valve in theopen position.

FIG. 7 is a cross-sectional view of a conventional gate valve in theclosed position.

DETAILED DESCRIPTION

It is to be understood that the following disclosure describes severalexemplary embodiments for implementing different features, structures,or functions of the invention. Exemplary embodiments of components,arrangements, and configurations are described below to simplify thepresent disclosure; however, these exemplary embodiments are providedmerely as examples and are not intended to limit the scope of theinvention. Additionally, the present disclosure may repeat referencenumerals and/or letters in the various exemplary embodiments and acrossthe Figures provided herein. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various exemplary embodiments and/or configurationsdiscussed in the various figures. Moreover, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed interposing the first and second features, suchthat the first and second features may not be in direct contact.Finally, the exemplary embodiments presented below may be combined inany combination of ways, i.e., any element from one exemplary embodimentmay be used in any other exemplary embodiment, without departing fromthe scope of the disclosure.

Additionally, certain terms are used throughout the followingdescription and claims to refer to particular components. As one skilledin the art will appreciate, various entities may refer to the samecomponent by different names, and as such, the naming convention for theelements described herein is not intended to limit the scope of theinvention, unless otherwise specifically defined herein. Further, thenaming convention used herein is not intended to distinguish betweencomponents that differ in name but not function. Additionally, in thefollowing discussion and in the claims, the terms “including” and“comprising” are used in an open-ended fashion, and thus should beinterpreted to mean “including, but not limited to.” All numericalvalues in this disclosure may be exact or approximate values unlessotherwise specifically stated. Accordingly, various embodiments of thedisclosure may deviate from the numbers, values, and ranges disclosedherein without departing from the intended scope. Furthermore, as it isused in the claims or specification, the term “or” is intended toencompass both exclusive and inclusive cases, i.e., “A or B” is intendedto be synonymous with “at least one of A and B,” unless otherwiseexpressly specified herein.

Referring initially to FIG. 1 , a gate valve assembly is formed from avalve body 3 which has an upstream passage 2 and a downstream passage 1.Both the upstream passage 2 and the downstream passage 1 areconcentrically located to each other and allow the medium (i.e., fluidsand mix) to pass through the valve body 3 in the open position. Fluidsand mix can enter from the upstream passage 2 and exit the downstreampassage 1. Alternatively, the fluid sand mix can enter from thedownstream passage 1 and exit the upstream passage 2 in the openposition.

Piston pocket 16 is formed into the valve body 3 and locatedconcentrically to the upstream passage 2 at the upstream passage 2 sideof the valve body 3. As shown in a close-up view in FIG. 2 , a piston 10is located concentrically to the piston pocket 16 and is disposedpartially within the piston pocket 16. The piston 10 includes a crown10A and a skirt 10B. The skirt 10B has an outside groove 21A tocooperate with an outside diameter (OD) seal or O-ring 21 and an insidegroove 22A to cooperate with an inside diameter (ID) seal or O-ring 22.Preferably the piston 10 is formed as a single piece.

A piston pocket hydraulic recess 14 is located at the base of the pistonpocket 16 and opposite the bottom surface 10C of the skirt 10B and has ahydraulic port 8 that intersects the piston pocket hydraulic recess 14.The hydraulic port 8 has an opening located on the exterior face of thevalve body 3. Needle valve 20 is fixedly attached to the opening of thehydraulic port 8.

When the gate valve assembly is in the open or closed position,hydraulic pressure is pumped through needle valve 20 via an externalhydraulic pressure source 23. The hydraulic pressure travels through thehydraulic port 8 and fills the piston pocket hydraulic recess 14, and inturn the hydraulic pressure moves the piston 10 outwardly from thepiston pocket 16 towards the downstream passage 1 of the valve body 3.The piston 10 has the OD O-ring 21 and the ID O-ring 22, which stop thehydraulic pressure from communicating with the downstream passage 1, theupstream passage 2, and the backside valve cavity 19. The backside valvecavity 19 is formed in a channel 5A that contains gate 5, such as areshown in FIG. 3 .

Referring to FIG. 4 , the valve assembly is shown in the closedposition. When the well pressure enters the downstream passage 1 of thevalve body 3, the downstream 1 side of the gate 5 will move towards theupstream passage 2 and will move an upstream seat 7 towards the upstreampassage 2, which will in turn move the piston 10 back into the pistonpocket 16. Additionally, the hydraulic pressure is pushed from thepiston pocket hydraulic recess 14, through the hydraulic port 8, andthrough the needle valve 20 and is in turn returned to the hydraulicpressure source 23.

When the gate valve assembly is in the open position, the fluid sand mixenters the valve body 3 from the upstream passage 2 through the valvebody 3 and exits through the downstream passage 1. Alternatively, in theopen position, the fluid sand mix can enter the valve body 3 from thedownstream passage 1 through the valve body 3 and can exit through theupstream passage 2. When the valve assembly is in the open position asshown in FIGS. 1, 2 and 3 , pressure is applied via the hydraulicpressure source 23, the piston 10 is forced towards the downstreampassage 1. The piston 10 is then forced onto the upstream passage 2 sideof the upstream seat 7. The upstream seat 7 is forced onto the upstreamside of the gate 5. The downstream side of the gate 5 is forced onto theupstream side of a downstream seat 6. The downstream seat 6 is thenforced onto a downstream seat pocket 15. A piston seat sealing surface11, the upstream side of the gate 5, the gate seat sealing surface 4,the downstream gate seat sealing surface 13, and a downstream seatpocket seat sealing surface 12 are now sealed. Fluid sand mix cannotpass into the backside valve cavity 19. (During the operation ofconventional gate valves in the open position as noted herein, the fluidsand mix will enter the backside of the valve cavity, which can causecatastrophic damage to the valve.)

Once it is time to change the position of the valve assembly from theopen position as shown in FIG. 3 to the closed position shown in FIG. 4, the hydraulic pressure is released from the hydraulic pressure source23. Piston 10, upstream seat 7, gate 5, and downstream seat 6 will nowhave no pressure forcing them to be compressed together, so in turnpiston seat sealing surface 11, upstream gate seat sealing surface 4,downstream gate seat sealing surface 13, and downstream seat pocket seatsealing surface 12 will now unseal.

The hydraulic ram assembly 17 can now be functioned to the closedposition. The hydraulic ram assembly 17 will move the valve stem 18 andgate 5 into the closed position. It will be understood that the gate 5can also be moved manually as those familiar with the art willunderstand.

When the gate 5 is moved into its closed position as shown in FIGS. 4and 5 , the hydraulic pressure source 23 can now be energized. When thegate valve assembly is in the closed position, pressure is applied viathe hydraulic pressure source 23, the piston 10 is forced towards thedownstream passage 1. The piston 10 is then forced onto the upstreampassage 2 side of the upstream seat 7. The upstream seat 7 is forcedonto the upstream side of the gate 5. The downstream side of the gate 5is forced onto the upstream side of the downstream side of thedownstream seat 6. The downstream seat 6 is then forced onto thedownstream seat pocket 15. The piston seat sealing surface 11, upstreamgate seat sealing surface 4, downstream gate seat sealing surface 13,and downstream seat pocket seat sealing surface 12 are now sealed. Fluidsand mix cannot pass into the backside valve cavity 19. (During theoperation of conventional gate valves in the closed position as notedherein, the fluid sand mix will enter the backside of the valve cavity,which can cause catastrophic damage to the valve.)

When moving the valve assembly from the open to closed position andclosed to open position, the hydraulic pressure from the hydraulicpressure source 23 will be released.

In contrast to the disclosed gate valve assembly and as noted previouslywith reference to FIG. 6 showing a conventional valve assembly in theopen position, fluid sand mix can enter from the upstream passage 30 andexit the downstream passage 29 in the conventional valve assembly.Alternatively, the fluid sand mix can enter from the downstream passage29 and exit the upstream passage 30 in the open position.

In particular and unlike the currently disclosed embodiment shown inFIG. 1 , the fluid sand mix in the conventional valve assembly of FIG. 6can enter the upper backside void 26 and the lower backside void 32because there is no sealing and because there is a gap between upstreamseat pocket 37, upstream seat 27, gate 25, downstream seat 33, anddownstream seat pocket 38. The fluid sand mix can now enter the upperbackside void 26 and the lower backside void 32 in the conventionalvalve assembly of FIG. 6 and can damage the upper valve stem packing 24and lower valve stem packing 34. Once both upper valve stem packing 24and lower valve stem packing 34 are damaged, the conventional gate valvewill leak to the outside of valve body 31.

As also noted, the fluid sand mix enters the upper backside void 26 andthe lower backside void 32 under very high pressure and velocity, whichin turn causes the sealing faces and components to erode due to a“sandblasting” effect.

As noted previously, another common failure of a conventional gate valveis when the fluid sand mix enters the upper backside void 26 and thelower backside void 32 under very high pressure and velocity and “packsoff” within the upper backside void 26 and the lower backside void 32,which stops the gate 25 from moving between the open position as shownin FIG. 6 and closed position as shown in FIG. 7 .

As noted previously with reference to FIG. 7 showing the conventionalgate valve in the closed position, when the fluid sand mix enters thevalve body 31 through the upstream passage 30, the gate 25 is pushed upagainst the downstream seat 33 and downstream seat pocket 38. A seal isformed between gate 25, downstream seat 33, and downstream seat pocket38. The fluid sand mix now cannot communicate with the downstreampassage 29. However, a gap is created between upstream seat pocket 37,upstream seat 27, and upstream passage side of gate 25. The fluid sandmix can now enter the upper backside void 26 and the lower backside void32, which will cause the conventional gate valve to fail as it would inthe open position.

When the fluid sand mix enters the valve body 31 through the downstreampassage 29, the gate 25 is pushed up against the upstream seat 27 andupstream seat pocket 37. A seal is formed between gate 25, upstream seat27 and upstream seat pocket 37. The fluid sand mix now cannotcommunicate with the upstream passage 30. However, a gap is createdbetween downstream seat pocket 38, downstream seat 33, and downstreampassage 29 side of gate 25. The fluid sand mix can now enter the upperbackside void 26 and the lower backside void 32, which will cause theconventional gate valve to fail as it would in the open position.

Shown in FIGS. 3 and 4 , if the hydraulic pressure source 23 fails todeliver pressure or it is desired to use the currently disclosedembodiment as a conventional valve with no hydraulic pressure, the gatevalve assembly is still capable of sealing in the closed position. Whenpressure enters the gate valve assembly from the upstream passage 2, thegate 5 will be forced against the downstream seat 6, and the downstreamseat 6 will be forced against the downstream seat pocket 15. Thedownstream gate seat sealing surface 13 and downstream seat pocket seatsealing surface 12 will now seal. Fluid sand mix can now not travel fromthe upstream passage 2 through to the downstream passage 1, and the gatevalve assembly is effectively closed.

When pressure enters the gate valve assembly from the downstream passage1, the gate 5 will be forced against the upstream seat 7 and theupstream seat 7 will be forced against the piston 10. The upstream gateseat sealing surface 4, piston seat sealing surface 11, and valve bodyseat sealing surface 9 will now seal. OD O-ring 21 and ID O-ring 22 willprevent the fluid sand mix from getting past the piston 10 and into thepiston pocket hydraulic recess 14 and the upstream passage 2. Fluid sandmix can now not travel from the downstream passage 1 through to theupstream passage 2, and the gate valve assembly is effectively closed.

The hydraulic valve assembly has a secondary safety feature to ensurethat the gate valve assembly will seal and to ensure that the fluid sandmix cannot exit the valve body 3 in both the closed and open position.Shown in FIG. 2 , if the OD 21 fails to seal, the needle valve 20 shownin FIG. 1 can be closed, which will isolate the hydraulic pressuresource 23. This action ensures that the fluid sand mix cannot exit thevalve body 3 and ensures that the gate valve assembly can continue to beused in a conventional manner similar to a conventional gate valve.

If the ID O-ring 22 and OD O-ring 21 have failed to seal when wellborepressure was entering the downstream passage 1 while the valve is in theclosed position, the gate valve assembly disclosed herein would stillact the same way as a conventional gate valve. Needle valve 20 will bein the closed position. The pressure entering the valve body 3 throughthe downstream passage 2 would force the gate 5 to be pushed towards theupstream seat 7. The upstream seat 7 would be forced up to piston 10.Piston 10 would be forced into piston pocket 16. Valve body seat sealingsurface 9, piston seat sealing surface 11, and upstream gate seatsealing surface 4 will now seal.

The piston seat sealing surface is illustrated as a groove 11A in theupstream 7 with a seal 11B to cooperate with the planar crown 10A. In analternative, the groove 11A can be formed in the piston crown 10A, withthe upstream seat 7 being planar.

The use of the piston 10 with the skirt 10B having an outside groove 21Aand an inside groove 22A to receive OD O-ring 21 and ID O-ring 22 allowshydraulic pressure to be used to seal the seats 6, 7 and the gate 5 sothat the fluid sand mix cannot enter the backside valve cavity 19 todefeat operation when the gate 5 is open or closed. When hydraulicpressure is not applied to the piston 10, the valve operates in the samemanner as a conventional valve where fluid sand mix can enter thebackside cavity 19 when the valve is closed.

While the disclosure is susceptible to various modifications andalternative forms, specific embodiments thereof are shown by way ofexample in the drawings and description. It should be understood,however, that the drawings and detailed description thereto are notintended to limit the disclosure to the particular form disclosed, buton the contrary, the intention is to cover all modifications,equivalents and alternatives falling within the spirit and scope of thepresent disclosure.

1-13. (canceled)
 14. A gate valve comprising: a body defining a bore, achannel, and a port, the bore defined through the body for fluid flow,the channel defined in the body relative to the bore, the port definedin the body for communication of hydraulic pressure; first and secondseat surfaces disposed in the bore respectively on first and secondsides of the channel; a gate being movable in the channel in sealingengagement relative to the first and second seat surfaces and beingconfigured to selectively permit and prevent the fluid flow through thebore; and a piston surface being sealed in communication with thehydraulic pressure from the port, the piston surface being movablerelative to the first seat surface in response to the hydraulic pressureand being configured to adjust a force of the sealing engagement atleast between the first seat surface and the gate.
 15. The gate valve ofclaim 14, wherein the bore defines first and second recesses beingrecessed from the bore and disposed respectively on the first and secondsides of the channel, the first recess having a first seat disposedtherein, the first seat having the first seat surface adjacent to thegate, the second recess having a second seat disposed therein, thesecond seat having the second seat surface disposed adjacent to thegate.
 16. The gate valve of claim 15, wherein each of the first andsecond seats in the respective first and second recesses comprises aseal disposed about an outside dimension of the respective seat andbeing configured to seal with the respective recess.
 17. The gate valveof claim 15, wherein the gate defines a gate passage therethrough; andwherein each of the first and second seats defines a seat passagetherethrough, the seat passages communicating with the bore, the gatebeing movable relative to the first and second seat surfaces of thefirst and second seats at least between first and second states, thegate in the first state having the gate passage aligned with the seatpassages, the gate in the second state having the gate passagemisaligned with the seat passages.
 18. The gate valve of claim 15,wherein the port defined in the body communicates with a pocket definedin the body adjacent to the first recess, the pocket having the pistonsurface sealably disposed therein.
 19. The gate valve of claim 18,comprising a piston disposed in the pocket, a first portion of thepiston being configured to contact the first seat, a second portion ofthe piston being sealed in the pocket and having the piston surfaceexposed to the hydraulic pressure from the port, the first portion ofthe piston being urged into contact with the first seat in response tothe hydraulic pressure exposed against the piston surface.
 20. The gatevalve of claim 19, wherein the first portion of the piston comprises acrown configured to contact the first seat; and wherein the secondportion of the piston comprises a skirt extending from the crown. 21.The gate valve of claim 19, wherein the pocket has an internal facingwall that is recessed from the bore and has an external facing wall thatfaces the internal facing wall and is radially separated from theinternal facing wall; and wherein the piston comprises: a first seal insealed engagement with the internal facing wall of the pocket; and asecond seal in sealed engagement with the external facing wall of thepocket.
 22. The gate valve of claim 21, wherein the first seal comprisesa first O-ring seal disposed about an outside surface of the piston; andwherein the second seal comprises a second O-ring seal disposed about aninside surface of the piston.
 23. The gate valve of claim 19, furthercomprising a seal configured to seal between the first portion of thepiston and the first seat.
 24. The gate valve of claim 23, wherein theseal comprises an annular seal disposed in an annular groove defined onan end of the first seat.
 25. The gate valve of claim 14, furthercomprising a control valve being connected to the port and beingconfigured to control communication of the hydraulic pressure with thepiston surface.
 26. A sealing apparatus for use in a gate valve havingfirst and second seats disposed in a bore of a body of the gate valveand disposed on opposing sides of a gate movable in the gate valverelative to the first and second seats, the sealing apparatuscomprising: a control valve being configured to communicate hydraulicpressure to an area of the bore adjacent the first seat; and a pistonbeing insertable in the bore in the area adjacent to the first seat, thepiston having first and second surfaces, the first surface beingconfigured to contact the first seat, the second surface beingconfigured to communicate with the hydraulic pressure from the controlvalve, the piston being movable in a direction of the bore relative tothe first seat in response to the hydraulic pressure from the controlvalve against the second surface of the piston.
 27. The sealingapparatus of claim 26, wherein the piston comprises: a crown having thefirst surface; a skirt extending from the crown opposite the firstsurface and having the second surface; a first seal disposed about anoutside dimension of the piston and configured to sealably engage withan internal facing wall of the area of the bore; and a second sealdisposed about an inside dimension of the skirt on the piston andconfigured to sealably engage with an external facing wall of the areaof the bore.
 28. A method to configure a gate valve having first andsecond seats disposed in a bore of a body of the gate valve, the firstand second seats disposed in recesses on opposing sides of a gate, thegate being movable in the gate valve in sealing engagement relative tothe first and second seats, the method comprising: defining an annularpocket adjacent to the recess for the first seat; defining a port in thebody to communicate hydraulic pressure with the annular pocket;installing a piston surface in sealed engagement in the annular pocketand exposed in fluid communication with the port; and installing thefirst seat in the recess of the bore between the gate and the pistonsurface.
 29. The method of claim 28, wherein defining the annular pocketin the bore adjacent to the recess for the first seat comprises: formingan internal facing wall of the annular pocket that is adjacent to therecess for the first seat and that is recessed from the bore; andforming an external facing wall of the annular pocket that faces theinternal facing wall and that is radially spaced from the internalfacing wall.
 30. The method of claim 29, wherein installing the pistonsurface in sealed engagement in the annular pocket and exposed in fluidcommunication with the port comprises: engaging an external seal of thepiston surface with the internal facing wall of the annular pocket; andengaging an internal seal of the piston surface with the external facingwall of the annular pocket.
 31. A method of operating a gate valvehaving first and second seat surfaces disposed in a bore of a body ofthe gate valve, the first and second seat surface disposed on opposingsides of a gate, the gate being movable in the gate valve, the methodcomprising: moving the gate in the gate valve in sealing engagementrelative to the first and second seat surfaces in the bore;communicating hydraulic pressure via a port defined in the gate valveagainst a piston surface disposed adjacent to the first seat surface inthe bore; and adjusting a force in the sealing engagement at leastbetween the first seat surface and the gate by urging the first seatsurface against the gate in response to the hydraulic pressurecommunicated against the piston surface.
 32. The method of claim 31,wherein communicating the hydraulic pressure via the port defined in thegate valve against the piston surface disposed adjacent to the firstseat surface in the bore comprises: communicating the hydraulic pressurevia the port to an annular pocket defined in the body; and sealing thehydraulic pressure in the annular pocket against the piston surface byusing an external seal of the piston surface engaged with an internalfacing wall of the annular pocket and using an internal seal of thepiston surface engaged with an external facing wall of the annularpocket.
 33. The method of claim 31, wherein adjusting the force in thesealing engagement at least between the first seat surface and the gateby urging the first seat surface against the gate in response to thehydraulic pressure communicated against the piston surface comprisesmoving the piston surface in a direction of the bore toward the firstseat surface in response to the hydraulic pressure communicated via theport to the piston surface.